The present invention relates to a transparent polycarbonate resin which has impact resistance, a high refractive index and reciprocal dispersion value and a low photoelastic constant and is excellent in terms of heat resistance and hue, a production method for the same, a resin composition comprising the same and optical molded articles of the same.
Since a polycarbonate resin has excellent mechanical properties such as impact resistance and also excellent heat resistance and transparency, it is widely used in many fields as an engineering plastic. As it is excellent in transparency in particular, it is used in lenses, prisms, optical disk substrates and the like as a plastic optical material.
To produce the polycarbonate resin, there have been known such methods as one in which an aromatic dihydroxy compound such as bisphenol A and phosgene are reacted with each other directly in the presence of an acid coupling agent, one in which an aromatic dihydroxy compound such as bisphenol A and a carbonic acid diester such as diphenyl carbonate are polycondensed through an ester exchange reaction in a molten state, and the like.
In either one of the above methods, a polycarbonate resin comprising only bisphenol A as an aromatic dihydroxy compound has a large photoelastic constant and relatively low melt fluidity, a molded article thereof has a large birefringence. Although the polycarbonate resin has a high refractive index of 1.58, it has a low Abbe number indicative of dispersibility of 30, which is a substantive defect of the material together with the above birefringence problem. Therefore, it has such a defect that it has not so high performance to be widely used in optical recording materials, optical lenses and the like.
The present inventors previously made an invention which relates to a polycarbonate resin having a structural unit derived from bisphenol having a spiro-ring skeleton, a production method for the same and a resin composition comprising the same (Japanese Patent Application Laid-open Nos. 2-214721 (1990) and 4-8761 (1992)). However, the structural unit having a spiro-ring skeleton structure is derived from 3,9-bis1,1-dimethyl-2-(4'-hydroxybenzoyloxy)ethyl!-2,4,8,10-tetraoxaspiro 5,5!-undecane, and the Abbe number of the polycarbonate resin is not satisfactory for use in optical lenses though it is better than that of a bisphenol A type polycarbonate.